JALTJIT. 291 



land rim of the atoll is only disturbed by the swell of the sea during a com- 

 paratively short time, while northwest winds are blowing. The island to 

 the north of Ai is connected with it by a narrow line of light green water, 

 through which rises, here and there, an occasional sand bank. 



The fine coral sand on the eastern face of the western land rim gradually 

 passes, on the beach facing the channel, into black shingle, and finally into 

 the beach rock conglomerate, which edges the beach on the western side of 

 the land rim. As we passed out, we noticed a series of spurs extending on 

 tlie reef flats at right angles to the outer reef line, and deflected in a direc- 

 tion parallel to the outer line of islets, thus forming an inner line of islands 

 similar to those south of the villas;e of Jabor. 



The charts of most of the atolls represent usually the sand spits, which 



are formed near all the passes, as at the southwest and southeast passes of 



Jaluit (Pis. 226, fig. 6 ; 228, fig. 2), and are so characteristic a feature of 



the passes leading into the atolls of the Marshall Islands (Pis. 226, fig. 6 ; 



•227, fig. 1; 228, figs. 3, 4). 



The sand spits or reef flats are extensive tracts on which Millepores and 

 Porites flourish. Where the corals reach the surface they are killed by 

 constant exposure to the air, NuUipores grow on the fragments of the dead 

 corals, which break off and gradually fill the interstices between the heads 

 and cliange the living reef flat to a bare flat covered with huge patches of 

 more or less coarse coral sand, with comparatively few living corals. The 

 existence of these sand spits formed on either side of the passages is often 

 indicated by the presence of a few small islands and islets running at right 

 angles to the general trend of the outer land rim. On the west side of the 

 atoll, as we steamed past it, we could see, near the centre of the western 

 face, the great wide flat extending far into the inner part of the lagoon 

 (PL 226, fig. 6), formed from the disintegration of a few larger islands still 

 to be seen either as islets or as low sand bars, some of them covered with 

 a little vegetation. The islands and islets on the wide lagoon flats and 

 shoals are arranged either in lines parallel to the outer land rim, or else 

 at right angles to its trend. 



When steaming along the western face of the atoll past the northern 

 extremity, we could, when looking across the narrow lagoon, note the number 



